Jul 26th 2007
From The Economist print edition
Worries about a population explosion have been replaced by fears of decline
 THE
population of bugs in a Petri dish typically increases in an S-shaped curve. To
start with, the line is flat because the colony is barely growing. Then the
slope rises ever more steeply as bacteria proliferate until it reaches an
inflection point. After that, the curve flattens out as the colony stops
growing.
Overcrowding and a shortage of resources constrain bug populations. The reasons
for the growth of the human population may be different, but the pattern may be
surprisingly similar. For thousands of years, the number of people in the world
inched up. Then there was a sudden spurt during the industrial revolution which
produced, between 1900 and 2000, a near-quadrupling of the world's population.
Numbers are still growing; but recently-it is impossible to know exactly
when-an inflection point seems to have been reached. The rate of population
increase began to slow. In more and more countries, women started having fewer
children than the number required to keep populations stable. Four out of nine
people already live in countries in which the fertility rate has dipped below
the replacement rate. Last year the United Nations said it thought the world's
average fertility would fall below replacement by 2025. Demographers expect the
global population to peak at around 10 billion (it is now 6.5 billion) by
mid-century.
As population predictions have changed in the past few years, so have
attitudes. The panic about resource constraints that prevailed during the 1970s
and 1980s, when the population was rising through the steep part of the
S-curve, has given way to a new concern: that the number of people in the world
is likely to start falling.
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